Antagonists: Constructing Dose-Response Curves

Finding pA2 From This Graph

If you remember, you find pA2 when:
log10(Dose Ratio - 1) = 0.
When looking at the graph, this is when y = 0.

So, from the graph, what is the value of pA2?
Click here to see lower left of graph in more detail.
(Click here to reshow full graph).

Type in your answer to one decimal place then press the OK button.

pA2 is: